In an optical digital audio disc (called a compact disc), the main channel consisting of a digital audio signal and a subchannel consisting of data for control, display or the like are recorded on spiral signal tracks. The processing for the error correction coding is performed with regard to the main channel and subchannel, respectively. Eight channels called P, Q, R, S, T, U, V, and W are defined in the subchannel. The P- and Q-channels among them are used for the selection of a program when the compact disc is played back. The display data or audio data is inserted in the other six channels or R to W. For example, the data for explaining a composer, performers and the like of music programs recorded in the main channel is recorded in the six channels of R to W.
The data in the subchannel includes control data such as indication of the kind of data actually recorded or instructions to process the data in the subchannel and the like. This control data is needed to indicate the subchannel or to accurately process the audio data, and its significance is higher than the display or audio data. Therefore, it is necessary to prevent errors from being included in the control data upon playback as possible. For instance, if only one bit of the control data becomes an error, the display data will have been erroneously processed as the audio data, so that this may cause a situation such that an abnormal sound is generated from a speaker.
As well as the data in the subchannel of the compact disc, there is a case where the kinds of data which are transmitted are not identical. For example, in a videotex system using a home use television receiver as a display device, there is a case where a control command is used as a special command other than commands representing fundamental elements in order to transmit graphic information through, i.e., existing telephone line network and optical transmission path.